Wars of attrition are won with factories, not bullets. The US manufacturing capabilities can no longer compete with all nations, and they are likely to continue that downward trend. Combine that with war machines that are very complex, and you have a very limited production speed.
The top tier equipment is often overpriced for what they deliver, and can't be rapidly replaced. The F35 is a good example. Super expensive per unit because it is a multi-purpose craft. Meaning it's not quite as good as a bomber, and not quite as good as a fighter, but way more expensive than eaither. I'm not even sure if the US has the capability to make one by itself. There's just no way they can 'pump them out' if it faced real adversity.
They are powerful aircraft, but they have a low power to cost ratio, and are exceptionally difficult to produce.
It doesn't matter if the F35 is able to take out 5 enemy craft for each one lost, if the enemy craft is 1/10th the cost and time to manufacture.
In a practical sense, China probably has the most dangerous air force. Each individual plane may be a shitty knock-off, but they can produce new ones faster than the US can mobilize existing forces.
Same, to a lesser extent, is true with Russia. Russia is often closer in ability though. The SU50 could (though probably not) even be a superior plane. It is more capable in maneuverability and radar detection, so who knows.
I think the US military has also realized this. I think that it the real impetus behind the light attack project. It is not just about saving cash, it's also a means of sustainable warfare. I think it will continue with light designs for other roles, as well as land and sea versions of the program.
I think it would depend on the goals of the conflict. The US would may not be able to raise the flag over Moscow or Beijing, but they couldn't do that in Washington either. It's said that neither Russia or China can project power far from their boarders, while the US can.
The most likely scenarios, say Russia invading Poland or China invading Taiwan, are still beyond Russia or China's capabilities, from what I've picked up from casual reading.